The answer is either the third or fourth option.
I want to go more with the fourth one though!!
Montesquieu believed in the separation of government into 3 branches with check and balances.
"Planting trees throughout Sahel" is the one action among the following actions given in the question that would be the most effective long-term solution to fighting desertification in the Sahel.
Subsidiary Alliance is a system by the East India Company. It solved the problem of ruling a nation which is under the rule of a king